Add ability to remove vaults from the app list without deleting files on disk,
and restore the bundled Getting Started demo vault when needed.
Changes:
- Rust: add hidden_defaults field to VaultList for tracking removed default vaults
- useVaultSwitcher: add removeVault() and restoreGettingStarted() with auto-switch
- useCommandRegistry: add 'Remove Vault from List' and 'Restore Getting Started Vault' commands
- StatusBar: add X button per vault item in vault menu dropdown
- 25 new tests covering removal, restore, edge cases, and command palette
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
